As a method of mounting a semiconductor chip on the mounting electrodes of a substrate having a wiring pattern formed thereon, a method is known in which solder bumps and solder precoating are applied beforehand on the semiconductor chip and the electrodes of the substrate and these solder portions (that is, the solder bumps and the solder precoating) are connected to each other, so that the semiconductor chip and the substrate are electrically and physically connected to each other. For the connection of solder, flux has been generally used. However, because of a finer connection pitch in recent years, particularly, a connection pitch smaller than 150 μm, it has been difficult to clean flux. Thus the mainstream of the connection of solder portions is to heat and melt solder without using flux after the semiconductor chip and the electrodes of the substrate are aligned with each other. After the connection of the solder portions, underfill resin is applied between the semiconductor chip and the substrate to reinforce solder joints and achieve reliability, and then the underfill resin is cured by heating, so that the mounting operation is completed.
In the foregoing connection method, however, when the solder joints melted during the connection are cooled thereafter, a shrinkage stress occurs due to variations in degree of shrinkage among members. Particularly, the stress is considerably concentrated on the outer portions of the connection electrodes of the semiconductor chip, so that cracks may occur on the connection electrodes of the semiconductor chip and the solder joints formed by melting the solder bumps, which has been a problem.
As a solution to this problem according to the prior art, a method of reducing a stress by containing resin particles in the solder (solder material) of solder bumps is available (for example, see Japanese Patent Laid-Open No. 2005-108871). FIG. 11 shows the structure of a solder bump of the prior art described in Japanese Patent Laid-Open No. 2005-108871. Reference numeral 20 denotes a solder bump, reference numeral 1 denotes the solder (solder material) of the solder bump 20, reference numeral 2 denotes a semiconductor chip, reference numeral 3 denotes the connection electrode of the semiconductor chip 2, and reference numeral 21 denotes resin particles. As shown in FIG. 11, the resin particles 21 are contained in the solder 1 of the solder bump 20 so as to be substantially evenly dispersed. The elasticity of the resin particles 21 reduces a stress occurring during cooling.